Conventionally, there has been known a turbocharger in which a turbine wheel is rotated by utilizing energy of exhaust gas introduced from an engine to rotate a compressor wheel disposed coaxially with the turbine wheel, so that pressurized air is supplied to an air-intake manifold, thereby improving output of the engine. In recent years, in the case where such a turbocharger is to be mounted on a vehicle, there is need for reduction of weight, cost-cutting, facilitation of manufacture, reduction of heat capacity, or the like. Thus, a turbine housing made of sheet metal has been increasingly used in the place of a conventional turbine housing made by casting.
As an example of a turbine housing made of sheet metal, Patent Document 1 discloses a turbine housing which includes a scroll part formed by bringing two right-and-left sheet metal members each having a plate-like shape or a bowl-like shape in contact with each other, and welding them in the circumferential direction, the scroll part having an exhaust gas flow path of a spiral shape formed inside. In addition, Patent Document 2 discloses a turbine housing including a housing of a scroll-like shape made of sheet metal and having an exhaust gas flow path of a spiral shape formed therein and an outer shell made of sheet metal, the outer shell being configured to cover the housing of a scroll-like shape.